Water Bodies and Stationary Current Conditions at Boundary Surfaces 461 



Figure 205 presents a dynamic section from Capetown towards the south-west based 

 on the "Meteor" observations (profile 1 a, 8-12 July 1925). The distribution of the 

 specific volume anomaly gives the structure shown schematically in Fig. 204. With this 

 stratification it can be expected theoretically (for the Southern Hemisphere) that there 

 will be a current flowing WNW to ESE just south of Africa (St. 20) and further 



Fig. 205. Specific volume anomaly in a cross-section south-west of Capetown ("Meteor" 

 profile 8-12 July 1925, 34^ 49' S., 17° 48' E. to 4V 12' S., 11° 31' E.). 



south (St. 18) there should be a current from ESE to WNW, if there is no motion 

 in the central region of the lighter water body. The observations show, however, that 

 this is not the case. According to dynamic calculations of the pressure field (Fig. 206) 

 there is a high-pressure ridge in the region of the central lighter water sloping down- 

 wards to the WNW in the northern part and to the ESE in the southern part. The system 

 of forces in the simple case of Fig. 204 is thus superseded by another pressure 

 system, which modifies conditions. It must be sufficiently strong to be able to reverse the 

 effect of the weaker opposite pressure gradient. These conditions can be represented in 

 a schematic way as shown in Fig. 207. Everywhere over the whole area the isobaric 

 surfaces and the physical sea level decline outwards though this is less so in the heavier 

 water masses than in the lighter central water. The current velocity in the heavier 

 water masses is thus less than in the lighter one in the middle. On the total northern side 

 there is a current from the east (the Agulhas Current), and on the entire southern side 

 is a current from the west (the West Wind Drift). The rule for a boundary surface 

 slope is now fulfilled ; since always when looking from the heavier towards the lighter 

 water the first moves towards the left relative to the latter (Southern Hemisphere). 



Of particular interest is the application of the rule for the position of the boundary 

 surface between water bodies in subtropical and tropical seas, where the upper part 

 of the troposphere is to a large extent separated into two layers. The tropospheric 

 discontinuity layer separates an almost homogeneous top layer from the subtropo- 

 spheric water masses of only slightly diff'erent density. Here, in places, the transition 



